Monday, October 19, 2009

Quantum mechanics seems alien to physiology. Alarm bells go off in our heads when we hear even people of such genius as Sir Roger Penrose (1) invoke the weird coherence of quantum mechanical wave functions to explain biological function. Of course, it is only some of the “weirder” parts of quantum mechanics that bother us. Structural biochemistry is founded on the rigid geometrical relationships involved in chemical bonding that arise from quantum mechanics; the α-helix could only have been discovered by Pauling by acknowledging the power of quantum mechanical resonance to flatten the peptide bonding unit (2). Nevertheless, most modern biomolecular scientists view quantum mechanics much as deists view their God; it merely sets the stage for action and then classically understandable, largely deterministic, pictures take over. In this issue of PNAS Ishizaki and Fleming (3), by combining experimental and theoretical investigations, demonstrate that quantum coherence effects play a big role in light energy transport in photosynthetic green sulfur bacteria under physiological conditions. Quantum coherence allows a nonclassical simultaneous exploration of many paths of energy flow through the many chromophores of a light-harvesting complex, thereby significantly increasing the efficiency of the energy capture process, presumably helping the bacteria to survive in low light.

Three major stages in the evolution of our universe are written in the phases of hydrogen. After nucleosynthesis the universe was an ionized plasma of hydrogen and helium. As expansion cooled the universe, hydrogen went through a phase transition, rapidly becoming neutral and releasing the Cosmic Microwave Background light at a redshift of ~1089. High energy photons produced by the firrst stars and quasars later reionized the hydrogen in the inter galactic medium (IGM), forcing the universe back through a second extended and patchy phase transition referred to as the epoch of reionization (EoR).